1. Field of the Invention
The invention relates to a two-dimensional sensor arrangement for detecting locations in two or three dimensions, in particular for touchpads or touchscreens.
2. Description of Related Art
Touch-sensitive touchpads and touchscreens are highly popular for operating electronic devices, which is not least due to the comfort of controlling the devices by swiping gestures and similar operating patterns.
Touch-sensitive sensor arrays are nowadays typically used to determine the location of one or more items within a two-dimensional sensing zone, and such sensor arrays may be disposed in front of a display screen. This enables the user to select items within the sensing zone by touching with a finger or a touching utensil, such as a conductive stylus, to move or shift items on a screen by swiping, to select, increment, or decrement alphanumeric settings by swiping or scrolling, etc.
A touch-sensitive sensor array comprises an arrangement of a plurality of sensors which in case of capacitive sensor arrays, for example, are mostly implemented in the form of projected capacitive (PCAP) sensing cells. The sensing cells in turn are usually made up of two sensor electrodes, i.e. a first and a second sensor electrode which are spaced apart by an interspace, in particular a gap. In the region of a sensor gap, i.e. between the pair of electrodes, an electric field may be generated which will change in the event of a controlling touch so that an electrical touch signature can be detected at the electrodes. The two sensor electrodes can selectively assume the function of a transmitting electrode and a receiving electrode so that the touch signature can be detected at the receiving electrode.
Contact points which are connected to the electrodes and are typically arranged in a contact zone outside the sensing zone are used to connect the electrodes to an electronic controller unit. The controller unit can feed signals into the transmitting electrode and can receive signals from the receiving electrode to evaluate them with regard to a touch signature.
In practice, the electrodes, the contact points, and the interconnections therebetween are typically applied on a two-dimensional substrate, directly or indirectly, and are designed as conductive patterns, in particular as conductive areas.
Interconnection of the contact points with the electrodes, i.e. the electrical connection between the contact points and the electrodes is only rarely made in the particularly simple manner of associating exactly one electrode of a sensor to each contact point. This would result in a very great number of contact points equal to the number of sensor electrodes.
In practice, a great number of contact points would result in a number of drawbacks. On the one hand, high complexity of the conductor layers on a substrate would result, and therefore a high error rate and operational instability in general. This in particular includes high susceptibility to interference due to interference fields due to closely arranged connecting conductors, i.e. the density of conductive tracks. Furthermore, complex and error-prone contacting of the sensor array is required, and the connected control electronics is also highly complex due to the multiplicity of signal inputs and outputs. Moreover, a great number of contact points usually implies longer conductive tracks, which may impair the response time of the sensor array and which adds to complexity in manufacturing. Therefore, it is desirable to reduce the number of contact points.
In order to reduce the number of contact points, a contact point is often connected to a plurality of electrodes, but in such a way that each pair of electrodes of a sensor, that is to say each sensor continues to be associated with a unique pair of contact points.
To this end, a contact point must not be connected to two electrodes of the same sensor but only to a plurality of sensor electrodes each of which belong to a different sensor. Accordingly, the contact points may be divided into two sets: a first set comprising those contact points which are connected to first electrodes, and a second set which comprise those contact points which are connected to second electrodes. If the first set consists of a number M of contact points and the second set consists of a number N of contact points, this is referred to as an M:N interconnection. Sometimes, this is referred to as an interconnection in an M:N matrix.
An M:N interconnection of the sensor electrodes is often implemented by electrically connecting some of the electrodes not only in the contact zone but already in the sensing zone and then connecting such a combination of joined sensor electrodes to one of the contact points in the contact zone. In this context, it should be noted that the connection of a plurality of sensor electrodes is of course equivalent to the use of one and the same large-area electrode for a plurality of sensors.
If first electrodes are already interconnected in the sensing zone, only a smaller number of independent first electrodes will be left compared to the original number of first electrodes which corresponds to the number of sensors, and this smaller number is designated as R herein. Similarly, an interconnection of second electrodes in the sensing zone results in a reduced number of independent second electrodes, which is designated as a number S herein. This is then referred to as an R:S interconnection in the sensing zone. Thus, a total of R+S connecting conductors is obtained which extend to the contact zone.
In particularly simple arrangements, each of the R+S connecting conductors is directly connected to a contact point in the contact zone, so that a number of M=R contact points of the first set and a number of N=S contact points of the second set is found. Therefore, the number of contact points will be M+N=R+S. However, in most applications the number of contact points is further reduced by first making a further interconnection in the contact zone so as to obtain M+N<R+S connecting conductors which are then routed to the contact points.
The physical arrangement of the sensors in the sensing zone is often implemented in the form of a matrix, i.e. a number of K*L sensors is arranged in K columns and L rows (K:L matrix) in the sensing zone.
For a sensor arrangement in the form of a K:L matrix it is known to apply a number of K electrode strips in the column direction in a first layer on a substrate, and to arrange a number of L electrode strips in the row direction in a superposed second layer. In this way, only M=K contact points of the first set and N=L contact points of the second set are required for K*L sensors. However, a plurality of superimposed layers are required. In other words, the electrode strips in the column direction are crossing those in the row direction, as seen in a projection on the substrate surface.
A similar implementation is disclosed in U.S. Pat. No. 5,113,041, for example, which describes a device for determining the location of a stylus tip in two dimensions in units of spacing intervals in equidistantly spaced patterns of conductive strips. One set of such conductive strip patterns extends in the x-direction and a similar set extends in the y-direction, the two sets being separated by a thin layer of insulating material which should advantageously be designed so as to be as thin as possible. Accordingly, three superimposed layers are employed in the sensing zone: one layer for the strips in the x-direction, one layer for the strips in the y-direction, and an insulation layer disposed therebetween. The strips running in the x-direction are crossing the strips running in the y-direction.
U.S. Pat. No. 5,463,388 discloses a computer input device comprising electrodes arranged in a grid pattern, which are connected in rows and columns, some of the electrodes being interconnected to one another by lines. The lines intersect in the sensing zone. Accordingly, a plurality of superimposed layers are required at least at the crossing points in the sensing zone.
The aforementioned teachings include crossings in the sensing zone, or in other words they comprise a multilayered structure. A particular drawback of a multilayered structure is the complex manufacturing process. While in single-layered configurations only a single conductive material layer needs to be applied on a substrate, a multilayered structure requires to alternately apply conductive and insulating materials.
In the case of transparent sensor arrays, however, a multilayered structure is furthermore disadvantageous in terms of optical properties. Transparent sensor arrays are in particular arranged in front of a screen, as a touch-sensitive layer for producing touchscreens. A multilayered structure causes the sensor arrays to be thicker, so that transmittance is lower and the haze value which is a measure of the opacity of transparent samples is higher. Moreover, both conductive and insulating transparent materials are required at the same time, and the refractive indices thereof might be different, which may lead to loss in transmittance. All this affects the display characteristics of a touchscreen.
Crossings furthermore have the disadvantage that the intersecting conductive patterns form unwanted pseudo-sensing cells which may cause interference in the control electronics.
It has been known to make crossing-free, i.e. single-layered interconnections at least in the sensing zone, while intersecting structures are displaced to the contact zone or elsewhere. With this compromise, the number of contact points can be kept small: typical are M:N interconnections which in turn correspond to the physical arrangement of the sensors in K columns and L rows, i.e. M=K and N=L.
Such or similar teachings are found in part in U.S. Pat. No. 9,081,453; DE 20 2006 010 488 U1; U.S. Pat. No. 8,319,747 B2; DE 10 2011 122 110 A1; DE 11 2008 001 245 T5; DE 10 2008 050 215 A1; DE 10 2011 108 153 A1; US 2015/0261348 A1.
However, even if the crossing of conductive patterns is not implemented in the sensing zone but in the contact zone (peripheral area), the drawback of complex manufacturing remains. The crossing interconnections between conductive patterns need to be realized via the third dimension perpendicularly to the two-dimensional sensor area, so that a single two-dimensional layer is not sufficient to enable interconnection.
The aforementioned drawbacks also apply to an embodiment of U.S. Pat. No. 9,081,453 which discloses a sensor array with a sensor controller, since a controller is not a single-layered component.
Accordingly, a sensor arrangement which can be produced in a single layer would be desirable, in particular for producing sensor arrays by printing conductive material onto a substrate, e.g. by screen printing.
While in multilayered conductive layer structures as described above the electrode gaps are mostly defined vertically, by superposing two conductive areas which are galvanically separated from one another by an insulating layer, in single-layered conductive layer structures the gap is typically defined by a lateral spacing between two conductive areas applied on the same substrate, that is, for example, by a galvanically insulating gap (sensor gap).
US 2004/0125087 A1 and U.S. Pat. No. 8,754,662 B1 disclose sensor arrays which can be produced with a single layer of conductive material. However, these sensor arrays need to be improved in terms of the number of contact points.
Furthermore, single-layered sensor arrangements are known in which some of the electrodes are connected to the contact points in such a manner that interconnections are routed through gaps between first and second electrodes of other sensors. However, this leads to the creation of undesirable pseudo-sensing cells and may in particular result in interfering capacitances. This may lead to undesirable interferences in control and evaluation and a more complex control electronics may be required.
Moreover, some known sensor arrangements are only provided for a fixed number of columns and/or rows, so that the size of the sensor array is not scalable with the same positioning resolution. Against this background it would be advantageous to have interconnection patterns which allow the size of the sensor arrangement to be scaled for a defined resolution.
German patent applications DE 10 2015 112 317.7 and DE 10 2016 113 162.8 are hereby fully incorporated by reference.